2. Stream: an object that either delivers data to its destination (screen, file, etc.) or that takes data from a source (keyboard, file, etc.) –it acts as a buffer between the data source and destination Input stream: a stream that provides input to a program –System.in connects a program to the keyboard Output stream: a stream that accepts output from a program –System.out connects a program to the screen

3.  Byte based FileInputStream FileOutputStream  Character based Reader Writer

5.  InputStream, OutputStream, Reader, Writer are abstract classes  Need to create an instance of stream of a non-abstract type  Can wrap the streams to be more convenience in reading and writing ex. wrap FileWriter with processing streams  BufferedWriter  PrintWriter wrap FileReader with processing streams BufferedFileReader

6. Text Human readable,Not efficient in terms of time and space

7. (C) 2010 Pearson Education, Inc. All rights reserved.  The Reader and Writer abstract classes are Unicode two-byte, character-based streams.  Most of the byte-based streams have corresponding character-based concrete Reader or Writer classes.

8. A typical codesegment for opening a textfile for output: FileWriter out = new FileWriter("test.txt"); BufferedWriter b = new BufferedWriter(out); //istead of writing a character each step, can write a number of characte at the same time or write a line PrintWriter p = new PrintWriter(b); Or with anonymous (‘unnamed‘) objects: PrintWriter p = new PrintWriter( new BufferedWriter( new FileWriter("test.txt"))); CIS 068

9. Using FileReader is not very efficient. Better wrap it with BufferedReader: BufferedReader br = new BufferedReader( new FileReader(“name“)); Remark: BufferedReader contains the method readLine(), which is convenient for reading textfiles CIS 068

10.  Display the words separated by any of the following characters: space, new line (\n), period (.) or comma (,). String inputLine = keyboard.nextLine(); StringTokenizer wordFinder = new StringTokenizer(inputLine, " \n.,"); //the second argument is a string of the 4 delimiters while(wordFinder.hasMoreTokens()) { System.out.println(wordFinder.nextToken()); } Entering " Question,2b.or 20. " gives this output: Question 2b or 20

11. BufferedReader ◦ read(), readLine(), … none for parsing types ◦ needs StringTokenizer then wrapper class methods like Integer.parseInt(token )  Can Use Scanner with File instead: Scanner inFile = new Scanner(new File(“in.txt”));

12. Scanner inFile = new Scanner(new File(“in.txt")); int number; while (inFile.hasInt()) { number = inFile.nextInt(); // … }

13.  BufferedReader ◦ readLine() returns null ◦ read() returns -1  Scanner ◦ use hasNext() or hasNextLine() to check first ◦ nextInt(), hasNextInt(), …

14. BufferedReader inFile = … line = inFile.readline(); while (line != null) { // … line = inFile.readline(); } ------------------- Scanner inFile = … while (inFile.hasNextLine()) { line = infile.nextLine(); // … }

15. (C) 2010 Pearson Education, Inc. All rights reserved.  Character-based input and output can be performed with classes Scanner and Formatter.  Class Scanner is used extensively to input data from the keyboard. This class can also read data from a file.  Class Formatter enables formatted data to be output to any text-based stream in a manner similar to method System.out.printf.

16. (C) 2010 Pearson Education, Inc. All rights reserved.

21.  The constructor with two String arguments specifies an absolute or relative path and the file or directory to associate with the File object.  The constructor with File and String arguments uses an existing File object that specifies the parent directory of the file or directory specified by the String argument.  The fourth constructor uses a URI object to locate the file.  A Uniform Resource Identifier (URI) is a more general form of the Uniform Resource Locators (URLs) that are used to locate websites.  Figure 17.3 lists some common File methods. The  http://java.sun.com/javase/6 / docs/api/j ava/io/File.html http://java.sun.com/javase/6 / docs/api/j ava/io/File.html

22. (C) 2010 Pearson Education, Inc. All rights reserved.

24.  A SecurityException occurs if the user does not have permission to write data to the file.  A FileNotFoundException occurs if the file does not exist and a new file cannot be created.  static method System.exit terminates an application.  An argument of 0 indicates successful program termination.  A nonzero value, normally indicates that an error has occurred.  The argument is useful if the program is executed from a batch file on Windows or a shell script on UNIX/Linux/Mac OS X.

25. (C) 2010 Pearson Education, Inc. All rights reserved.

26.  Scanner method hasNext determines whether the end- of-file key combination has been entered.  A NoSuchElementException occurs if the data being read by a Scanner method is in the wrong format or if there is no more data to input.  Formatter method format works like System.out.printf  A FormatterClosedException occurs if the Formatter is closed when you attempt to output.  Formatter method close closes the file.  If method close is not called explicitly, the operating sys-tem normally will close the file when program execution terminates.

27. Efficient in terms of time and space Not readable

28. Class: FileInputStream/FileOutputStream... see FileReader/FileWriter The difference: No difference in usage, only in input/output format CIS 068

29.  You can also read and write objects to files  Object needs serialization  If an object is to be serialized: ◦ The class must be declared as public ◦ The class must implement Serializable ◦ The class must have a no-argument constructor ◦ All fields of the class must be serializable: either primitive types or serializable objects

30. ObjectOutputStream objectOut = new ObjectOutputStream( new FileOutputStream(fileName)); objectOut.writeObject(serializableObject); objectOut.close( );

31. ObjectInputStream objectIn = new ObjectInputStream( new FileInputStream(fileName)); myObject = (ObjectType)objectIn.readObject( ); objectIn.close( );

32. try{ while (true) //readoject } catch (EOFException e)

33. (C) 2010 Pearson Education, Inc. All rights reserved.

37.  ObjectInputStream method readObject reads an Object from a file.  Method readObject throws an EOFException if an attempt is made to read beyond the end of the file.  Method readObject throws a ClassNotFoundException if the class for the object being read cannot be located.

38.  A stream is an expensive resource  There is a limit on the number of streams that you can have open at one time  You should not have more than one stream open on the same file  You must close a stream before you can open it again  Remember to close your streams!

39. (C) 2010 Pearson Education, Inc. All rights reserved.  Interface DataOutput describes a set of methods for writing primitive types to an output stream.  Classes DataOutputStream (a subclass of FilterOutputStream ) and RandomAccessFile each implement this interface to write primitive-type values as bytes.

40. (C) 2010 Pearson Education, Inc. All rights reserved.  Class JFileChooser displays a dialog that enables the user to easily select files or directories.